Eurodesk SL2442FX-Pro Mixer - No Output

[efsnick]

Hello,

I have a Eurodesk SL2442FX-Pro Mixer that a friend gave me and im trying to fix so my band can use it. The board has no output on the mono, left or right main outputs. The only place I have an output is in the head phones. I checked the main slider but it seems to be Ok....I have this thing cracked open, but there are no obvious answers. Any ideas? confused:

[Enzo]

How did you check the main sliders?

DO any of the AUX sends work? FX send? SUb outs? You said nothing works but the headphones, is that true or just sorta?

Have you tried channels all up and down the board, or just the first few to determine nothing was happeneing? It is possible 23,24 work while 1-16 do not.

Apply a signal to a channel and set it up so the signal should be hitting the master. Make it a pretty strong full signal. Now check the main LR slider. Slide it maybe 3/4 up. Oh who cares, all the way up is fine too. You should be able to find the pins of that slider sticking through the board. Scope it. You get signal on the hot ends? No scope? set your meter to AC volts and look for signal with it. Remember at this point we don;t care what it sounds like, we just want something coming out. Detecting the presence of hte signal is enough.

Do your group outs work? Do your main out inserts work? As sends? as returns?

If you stick a signal into the master insert, does it then come out the mono? Since the mono works off the masters signals, if they get no signal, neither will the mono.


If nothing is getting to the master sliders, turn them up and touch the various pins of it with your fingers. Does that produce hum in the output? Could be the master section works but is simply not getting signal.

And where are you located?

[efsnick]

I actually only pulled out the main slider and tested it in another circuit of mine as a dimmer and tested the resistance on it. Seemed to be ok.


Ok, so the Aux and Fx sends are giving off a signal when I plug into any of the 24 channels, its in mono but still there. I was able to get the main and mono outputs to work only when plugging a signal into the main inserts. No luck on the other 24 channels though. When I plugged a beat machine into the Main inserts, I got a signal from the left and right main outs, but I could not control it with the main slider. When I plugged my output to the mono channel I could control the output with the mono slider. Sub hannels 1 and 2 are the only ones I can adjust and get to work in the subs group.

Sub 3, 4 and the main sliders are the only ones I can not get to adjust. I guess my problem is there huh?

I have not checked to see if there is signal at the slider pins yet, due to my meter being shorted, so I will have to do that later if you dont have enough info yet.


I am in North Carolina btw

I really appreciate your time, Thanks

[Enzo]

The inserts are after the master slider but before the main outputs. SO the main outputs work. I'll believe your slider is OK.

I am now thinking you probably have a bad op amp IC. I will have to download the files to determine which one it is.

Are you ready to do surface mount solder work?

[efsnick]

As in am I capable?? ha ha I hope so?! We played around with op amps a little in my Linear IC class, but that just means I know enough to be dangerous. If I had a schematic I could try to run it down myself, but I know behringers rules and you probably know right where to go. Thanks for looking it up for me!

[Enzo]

Surface mount means the tiny ICs that solder right on the top of the board, not the older larger ICs whose legs go through holes in the board and are soldered on the other side.

Have you looked at your board? AM I right, most of the parts do not stick through holes?

[efsnick]

Crap, your right they are surface mount, I was just assuming other wise based on how easy it was to pop the slider in and out. I think I can handle it, as long as im pointed in the general direction. Should I worry?

[Enzo]

Not a matter of worry, it is a matter of whether you are willling and able to do it. I am not a big fan of soldering that stuff, and I have been soldering for over 50 years.

[efsnick]

50 years huh? Maybe I will get one of my instructors to do it for me. Are there rules against passing along a schematic even if the item is discontinued with behringer, I hate putting you out on this. But once again you can probably run it down faster than I.

[Enzo]

Before we go much further, are you familier with this deck? Have you assigned the signals?

Each channel has assign buttons. You can take channel 1 for example and assign it to the main mix, or to subs 1/2, or to subs 3/4. Or all of them even. Make sure to assign a channel to the mains. Likewise the four subs. They operate independently, so if you want them in teh mai out, you have to assign them to it. If 3/4 won;t do anything, make sure they are assigned to main out.

Meanwhile all four subs should appear on the sub out jacks - please check - as long as the input channel is assigned to all four. In other words, whatever sub groups have inputs assigned to them should show that input on the sub out jack.

But assuming you have all that going on...

I will describe the signal path. Apply a test signal and trace it through the subsections.

The subs are configured in pairs, and dual op amps are used, so in each stage 1/2 of the op amp serves each sub. (# means IC#) SO subs 1 and 2: from the sub bus, through #41, sub fader, #48, #52. With mute transistors T45, T46 for subs 1 and 2 respectively.

SUbs 3/4 similar, from bus: #43, sub fader, #50, #54, with mute transistors T47,T48.

SO #41 for example IC41A for sub 1 and IC41B for sub 2.

That should see output from each sub out for an assigned input.

From there, the subs can also be assigned to the main LR mix. That feeds to the graphic EQ. Turn the graphic off - set the switch for EQ OUT. IC#44 carries the signal past the EQ.

From there the L/R signal goes through the MAIN/MON switch. Toggle that back and forth to see if it is just dirty. Also the EQ IN/OUT switch is right there. Either one of those switches could kill the main L/R.

FInally the main outs, starts with the MAIN L/R insert jacks, then the main faders (I had that backwards apparently), through #45, #51, and on out the jacks.

That describes hee signal path. They are all common dual op amps, meaning their output pins are 1 and 7. I'd go down the row of them and see if any output pins are sitting at a large DC offset. Not worried about a few millivolts but 10v or 15v is not good.

After that, apply a signal and trace it along.

ON a large mixer like this, you have the master board or boards, which includes a few input channels, then the rest of the channels are add-on boards. For convenience, you can operate just the master. You can disconnect the several small short jumpers between the boards to free the master board. I mean disconnect the channel boards to the left of it. It still must be connected to the jack boards and such. Just everything to the left of the master board can go.

[efsnick]

I am familiar with the deck and have everything assigned as it should be.

I have not had a chance to measure the IC's you mentioned yet, but just messing around with controls, I notice that ANY channel I would hit solo on would peak out and produce a scratchy noise, whether I had a signal on it or not. Also when I would hit solo the output would be in mono If I had a signal applied and I get signal leaks from other inputs that are not in solo mode.

As I had mentioned before the signal is making it to the FX and AUX, I am able to hear it with my headphones. Also when I plug a signal in the main inserts the signal is making it to the mains.

Just wanted to pass this info along, I will let you know when I have tested the IC's.

[efsnick]

Ok, I have measured all of the outputs on the IC's you mentioned and I am getting no voltage. Am I doing it right? I hook the negative line of the meter to a ground and touch the output with the positive.

Also, to measure the DC offset with a volt meter, do I just short the non and inverting inputs together and measure the output?

[Enzo]

We don;t WANT to find DC voltage on those outputs normally, we are looking because if we find some, it usually indicates a failed IC. Sometimes life is that simple. Go down teh row, find one IC with 4v on the output (or whatever), change it out, and voila!

You don;t have to do anything at all to the circuit, this is not some sort of specification assessment like common mode rejection or something. If an output pin is supposed to sit at zero volts DC, and there is +15VDC there, then that is DC offset I refer to.

If you don;t find any signal path ICs with DC on their outputs, then that one particular troubleshooting effort didn;t pay off. Move on.

Apply a signal, set it up so it should be coming out the mains. Follow the signal at the output pins of the various ICs, and see where it disappears. That is why I listed the ICs as a description of the signal path.

As we mentioned, these things work in pairs, so one IC serves two channels. SO for example in subs 3/4, the left half of the IC serves 3 and the right half serves 4. ANd there would be however many ICs in the circuit overall.

The fact that you have lost both laft AND right or both 3 AND 4 leads me to suspect a bad IC. One IC can thus block two signal channels.

[efsnick]

Ok, so on IC51 I am showing a -15mv on the output of Op-A on Side b however -20v on Op-b's output, which is the same voltage as the non-inverting input on side b. No voltages on any other outputs throughout the circuit. Could that be it!?!

[Enzo]

DOubtful. I am worried about several volts, not a few millivolts. The DC thing is just a fast check for gross defects. Move on to signal tracing.

[efsnick]

Thats why I was saying the 2nd op amp in IC51 is Showing a large 20 volt output. Would that mean just one side, left or right would be out, not both?

[Enzo]

I am very sorry, my old eyes saw 15mv and then saw 20mv instead of 20v.

yes, I'd say 20v was not a good sign, especially if the input pins are not sitting at 20v. Most likely bad IC> Remove the IC and then see if the 20v appears on any of the vacant pads. I bet it doesn;t. In which case a new IC would probably cure that. But check all the others too. COuld be more than one bad.

But before you swap out ICs, verify the master slider is not open to its wiper contact. In other words, you have 20v at pin 7 and pin 5 of IC51, right? VR57B, half of the main mix fader is the ground return for IC51b. It connects to the wiper. Power down, and you should get a varying resistance to ground from pin 5 of IC51 as the fader is moved, same sort of reading as pin3 on the other side of 51. You tested the fader earlier, but the trace to it could be open.

[efsnick]

Ok, I swapped IC45, IC51. I am still getting the same voltages, but something I didnt notice before is that both IC's, on pins 4 and 8 are operating on -200v on both rails, unlike others that I measured where pin 4 was -200 and pin 8 +200. I think my issues lie elsewhere. Perhaps in the pin 8 + voltage feed?

[Mike C]

Did you check for output on the subgroup outs as suggested. If they do work those could be used to run your system. I hate to say it but Behringer is not the most durable or repair friendly of sound equipment.

Mike Caldwell
http://www.mikecaldwellaudioproductions.com

[efsnick]

Mike,

Yeah I tried the sub outs, I could only get a couple of them to work. I know behringer is far from the best, but you got to work with what you got.

ENZO,

For some reason my posts are not showing up all the time so I am reposting this one in case you see it twice.
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Ok, I swapped IC45, IC51. I am still getting the same voltages, but something I didnt notice before is that both IC's, on pins 4 and 8 are operating on -200v on both rails, unlike others that I measured where pin 4 was -200 and pin 8 +200. I think my issues lie elsewhere. Perhaps in the pin 8 + voltage feed?
-------------------------------

[Enzo]

You can't be having 200v on those ICs, or the whole mixer would be in flames.

However, if your ICs are missing one of the power rails, that would certainly cause the symptoms.

I don;t see any isolation resistors for those ICs. Pin 8 should show +15v. All the ICs I listed above in the master and subs circuits run directly off the +/-15v rails. SO if you have +15 on pin 8 of one, it SHOULD be there on all. If not, it would seem a lack of continuity is to blame. Check for power on all of the ones discussed, are the ones missing power all common to one area? Maybe the dead ones are on the jack board while hte live ones are onthe main board or something. if there is an open supply rail lead somewhere, a small jumper wire tacked from a live one to the dead ones ought to work. Make sure there is continuity between all the pins 8 of all the dead ones then.

[efsnick]

I guess I misread my meter, cause its saying -20 now. But yes the ones missing power(Negative on both rails) are common to one area. They are on the main board and they run from the Main slider all the way over to the SUB 1 slider, skipping the IC 42 row. Then also a couple above the master slider section near the talk back stuff. The rest are ok on the main board though.
I will try jumping a wire as suggested.

[efsnick]

Ok I jumped a +20 rail to IC45, IC51 pin 8 on both and I have the right main working! I am getting alot of static and clipping on the line though, but its a start I guess...

[Enzo]

Now that they are running, check pins 1 and 7 for DC. Just in case.

[efsnick]

Nope just a few millivolts like you said. I have +/- 15v on my rails now and my sliders are working. No more signal noise, think I was on a bad input. So should I go looking for the polarity problem or you think its ok to bypass? Also yesterday when I was measuring one of the master slider op amps I accidentally bridged a connection and something started smoking briefly up where the powersupply and digital effects meet. I couldnt see the source, but I lost my headphones signal and the polarity problem then occured on the opamp i was measuring. Can you tell where the positive rails originate?

[Enzo]

originate? I have no idea. The power supply provides the rails. How the traces are routed, I have no idea. SChematics don;t cover that.

What polarity problem are we talking about? if you mean the odd voltage on the pin that was missing its supply, no. When an IC should have +15 on one corner and -15 on the other, and say the +15 goes away, then the whole IC can appear to have -15 on it. But restore the +15 rail to it and it all balances out like it should.

Did subs 3/4 come back?

What specific problems remain?

Headphones: COmes out of all those selector switches, through a couple JFETs T38,T35, then through #33, CR/phones volume control #38, those doubling left right. From there we go to IC#1,2 one for each side of the phones.

If IC1,2 lack power, ther are a couple 22 ohm isolation resistors in the power rails, R41,R42.